AN INNOVATIVE PREFABRICATED PILE INSTALLATION METHODUTILIZING JETTING AND PRESSURE GROUTING

摘要

The majority of Florida Department of Transportation (FDOT) highway structures(e.g., bridges, signage, etc.) are founded on deep foundations, i.e., driven piles and drilledshafts. In the past, the most commonly used foundation type was driven piles. Withincreased urbanization, the noise and vibrations associated with pile driving has resultedin more drilled shaft usage due to its less intrusive characteristics. Unfortunately, due tohorizontal soil stress relief during installation, drilled shafts suffer reduced axial andtorsional resistance when compared to similar sized driven piles. Additionally, as-builtdrilled shaft integrity is generally more questionable than precast piles.To address these concerns, FDOT investigated post grouted drilled shaft tips, whichnot only increases the end bearing, but also proof tests every shaft. However, the issuesof quality control (i.e., the structural integrity of the cast-in-place shaft) and the reductionin side friction due to horizontal stress relaxation still remained. Thus, the FDOT fundeda research project to develop an innovative new deep foundation type which ensures boththe quality control of a precast member with the lateral stress increase similar to a drivenpile but with the minimum intrusion of a drilled shaft. It is referred to as a jet-groutedprecast pile or jet-grout pile.The research was conducted in FDOT’s new cylindrical 3.66 by 10.67 meter ingroundgeotechnical test chamber, which is capable of monitoring soil stresses anddeformations. The first trials involved jetting precast concrete piles with multiple sets ofembedded grout delivery pipes. The early tests revealed higher horizontal versus verticaldistribution of the compaction grout, as well as poor bonding between the grout and pile.Subsequently, the grout delivery system was re-designed; a new colloidal grout mix wasdeveloped along with the introduction of grout membranes on the outside of the pile.Small scale testing showed complete envelopment of the pile with excellent grout bond tothe pile.Finally, a full scale (0.406m×0.406m×6 m) pile was jetted and subsequentlygrouted along its length in two stages with no tip grouting. The pile was then torquetested to 610 kN-m with 15° of rotation, resulting in a unit torsional side resistance of 77kPa. Next, the tip of the pile was grouted and a top down compression test yielded 1,335kN of resistance at 0.25 mm of vertical pile head movement that exceeded the resistanceof a traditional similar size driven pile.